A surprise Senate race rises out west

Mr. Bennet noted his rival’s usual distaste for government spending, which the Republican has blamed for inflation.

“I hear he hates federal spending, except for the $14 million that built this thing,” said the incumbent, who was a surprise appointee to a Senate vacancy in 2009 before winning election for the first time in a difficult environment the next year.

Mr. O’Dea, standing near the heavy equipment his workers will employ to return a stretch of the imperiled river to its natural flow, was not impressed by the praise heaped upon Mr. Bennet by the assembled backers of the project.

“That’s what politicians do,” Mr. O’Dea said, making clear that he did not consider himself part of that cohort. “I’m into building things, and we will do our job here.”

Colorado was not expected to be part of the Senate battleground landscape this year. While not yet in the solid blue column, the state has been trending Democratic, and Mr. Bennet seemed a good bet for another term as Republicans invested their resources in what they saw as riper opportunities elsewhere.